Dr. Smith, Will and the Robot discover a spooky cave that contains a number of complex machines and an assembly line of some kind. When Smith fools around with the computer, the machines start up and the assembly line produces a cyborg. The cyborg comes to life and attacks Smith and the Robot, injuring the Robot very badly.
Smith runs screaming all the way back to the Jupiter 2. The cyborg follows him and Don and John kill it with their disintegrator net. When asked what happened to the Robot, Smith lies and says he doesn’t know. John is angry and confines Smith to the spaceship until he fesses up or the Robot comes back.
Dr. Smith sneaks out of the Jupiter 2 that night and goes back to the cave to fetch the Robot. The Robot is on the ground, too damaged to get up. In his zeal to wake him, Smith mistakenly bumps the computer and produces another cyborg. It chases Smith, intending to kill him, but when the doctor touches the computer again, the cyborg sudden becomes subservient. Smith is pleased with this turn of events, realizing that he can now create many slaves to do his bidding.
Smith does just that, and is soon being treated like a king with cyborgs preparing meals and dancing for him. He gets one of his new slaves to repair the Robot and then brags to the Robot about how he will first take control of the Jupiter 2, and then take control of the universe. Robot is not impressed.
Time passes, and the Robinsons, concerned about the whereabouts of Smith and the Robot, decide to begin searching in the morning. Will is too worried to wait that long and goes out to search on his own. He goes to the cave where he finds that Smith has created cyborg soldiers in his own image. The doctor explains to Will that he intends to conquer the universe, and Will is upset, thinking Smith has gone mad. Will wants to run home to warn his family, but Smith locks him up in a cell with the Robot instead.
In the morning, John and Don begin to search for their three missing crew members and are confronted by Dr. Smith who announces that he is now in command. When they protest, Smith sets one of his cyborg warriors on them. John and Don kill the cyborg, but are forced to back down when they realize Smith has an endless supply of soldiers at his command. John and Don go back to the Jupiter 2 to set up the force-field in case Smith and his army decide to attack.
Dr. Smith goes back to his cave to create an even more powerful breed of cyborg. Will and the Robot manage to escape from their cell, and Will runs to Smith, pleading for the doctor to see reason and change his mind. Smith accidently pushes Will onto the assembly line. Will gets caught up in one of the machines, and is turned into a cyborg with a face that matches Dr. Smith. Cyborg Will tells Smith he is no longer needed and will be destroyed. Smith is horrified and runs, screaming, back to the Jupiter 2.
When he arrives at the spaceship, Smith tells the others the terrible news, and John and Don rush to the rescue. Don is soon hurt, and John must fight his way past countless cyborg soldiers, but he bravely continues on. When he finally reaches the cave, he speaks to his son, but finds that neither Will’s mind (nor his face) are his own. John grabs Will and hauls him out of the cave while the Robot blasts the evil computer and its machines. With the alien technology destroyed, Will is returned to his normal self again. John is angry enough at Smith to eject him from camp, but the doctor proves to be so pathetic that John takes pity and offers him one last chance.
- In order to create the 'army' of Smith clones, casts were made of Jonathan Harris' face. Because of his claustrophobia, Harris was extremely frightened of carrying out such a procedure given that it would take around three hours to work, and was only able to go along with it thanks to the actions of the caster who tried to ease his fears.
- The reason why or how this considerable military industrial complex is hidden in a cave on an obscure planet is never given. Perhaps since supposed the same planet as in "Hunter's Moon" it has something to do with the Zahn.
- This is one of the few episodes where Smith's actions cause Prof. Robinson to exile him permanently from the expedition. Smith then shows apparently a genuinely contrite self-assessment of his actions, causing the Professor to give him another chance.
- If the computer and its machines were so easy to destroy, why didn’t the Robot blast them in the first place when he saw trouble brewing?
- Dr. Smith’s “Cyborg Chef” prepares him a lot of fancy food. Where did the food and the ingredients needed to make it come from? Where did the bowl of fresh Earth-fruit we see sitting on Smith’s dinner table come from?
- Who dresses these cyborgs and Why do they choose such silly costumes?
- Didn't Will and the Robot use that exact same ‘fake sick to fool the guard and escape from jail’ trick three episodes ago in “Kidnapped in Space?”
- How does that cyborg-making process work? Them seem to be created out of bread dough. Mmm... fresh baked cyborgs.
- Since Dr. Smith almost accidentally destroyed Will, it's a miracle that the Robinson's welcomed him back with open arms.